Improved yield or plant productivity is a desired horticultural effect on horticultural crops that is generally limited by the amount of light, temperature, relative humidity and other uncontrollable environmental factors when pests, water and nutrients are adequately controlled. Particulate matter from a wide range of sources is generally regarded as limiting plant productivity. See for example, Farmer, "The Effects of Dust on Vegetation--A Review," Environmental Pollution 79:63-75 (1993).
The prior art has discussed photosynthesis and the effects of environmental stresses on plants. See, for example; Nonomora and Benson, "Methods and compositions for enhancing carbon fixation in plants," U.S. Pat. No. 5,597,400, Stanhill, G., S. Moreshet, and M. Fuchs. "Effect of Increasing Foliage and Soil Reflectivity on the Yield and Water Use Efficiency of Grain Sorghum," Agronomy Journal 68:329-332 (1976); Moreshet, S., Y. Cohen, and M. Fuchs. "Effect of Increasing Foliage Reflectance on Yield, Growth, and Physiological Behavior of a Dryland Cotton Crop," Crop Science 19:863-868 (1979), which states that "within 2 days after spraying the kaolin reduced .sup.14 CO.sub.2 uptake (photosynthesis) by more than 20%" and "the kaolin sprays would appear to reduce transpiration more than photosynthesis"; Bar-Joseph, M. and J. Frenkel, "Spraying citrus plants with kaolin suspensions reduces colonization by the spiraea aphid (Aphis citricola van der Goot)" Crop Protection 2(3):371-374 (1983), which states that "The reasons for this [yield increase of Stanhill, Ibid. and Moeshet, Ibid.] are uncertain [because photosynthesis is reduced] but aphid and virus control may have contributed to this yield increase"; Rao, N. K. S., "The Effects of Antitranspirants on Leaf Water Status, Stomatal Resistance and Yield in Tomato," J. of Horticultural Science 60:89-92 (1985); Lipton, W. J., and F. Matoba, "Whitewashing to Prevent Sunburn of `Crenshaw` Melons," HortScience 6:434-345 (1971); Proctor, J. T. A. And L. L. Creasy "Effect of Supplementary Light on Anthocyanin Synthesis in `McIntosh` Apples," J. Amer. Soc. Hort. Sci 96:523-526 (1971); Lord, W. J, and D. W. Greene, "Effects of Summer Pruning on the Quality of `McIntosh` Apples," HortScience 17:372-373.
Therefore, there is still a need for cost effective inert, nontoxic methods for enhancing photosynthesis of horticultural crops. The prior art teaches away from the use of highly reflective inert particles of the instant invention in that increasing reflectivity reflects photosynthetically active light, thus, reducing photosynthesis. Unexpectedly, the instant invention results in an opposite effect--enhanced photosynthesis.